Believe it or not, most of our writers didn't enter the world sporting an @baseballprospectus.com address; with a few exceptions, they started out somewhere else. In an effort to up your reading pleasure while tipping our caps to some of the most illuminating work being done elsewhere on the internet, we'll be yielding the stage once a week to the best and brightest baseball writers, researchers and thinkers from outside of the BP umbrella. If you'd like to nominate a guest contributor (including yourself), please drop us a line.

Matt Lentzner has carved out a (very) small niche in the baseball analysis world by examining the intersection of physics and biomechanics. He has presented at the PITCHf/x conference in each of the last two years and has written articles for The Hardball Times, as well as a previous article for Baseball Prospectus. When he’s not writing, Matt works on his physics-based baseball simulator, which is so awesome and all-encompassing that it will likely never actually be finished, though it does provide the inspiration for most of his articles and presentations. In real life, he’s an IT Director at a small financial consulting company in the Silicon Valley and also runs a physical training gym in his backyard on the weekends.

Continuing to look at plate discipline with a discussion of contact rate and swing frequency.

Last Friday, I discussed plate discipline at length, noting that the commonly cited facet of performance extends beyond its synonym of patience and into the realm of making fewer responsive mistakes in a given trip to the dish. I introduced signal detection theory as a means of more accurately measuring which hitters produce the correct responses most often, since having good plate discipline must also cover the optimization of in zone pitches and not merely how often a hitter chases.

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Any hopes for success may be fading fast for this former highly touted Braves prospect.

Jeff Francoeur's career has been a series of ups and downs, the high point coming in his first year in the majors, and his lowest occurring this past season. To avoid becoming a has-been at age-25, Francoeur will need to figure out how to harness his talent. Today we'll take a look at what went wrong in his dreadful 2008, and what we can expect from him going forward.

Can the game's former best prospect bounce back and be a late-winter bargain as a free agent?

Sifting through the remaining free agents shows us that the available options are mostly part-time players, guys coming off of disappointing campaigns, or Barry Bonds. It's not clear which non-Bonds classification Corey Patterson belongs to yet, considering some of the seasons he's had in the past are on both the positive and negative ends of the production spectrum. Is Patterson still capable of a few more productive seasons, or is he more likely to be a speedy fourth outfielder from here on out?

How different ballparks affect velocity, whether pitchers use the fastball more early in games, and the challenge of quantifying plate discipline.

"Plate discipline though is difficult to measure. Good plate discipline can mean swinging at the first pitch, fouling off the fifth, taking the tenth; it's about hitting when it's possible to do so and walking when not. If it's possible to hit, a walk is a relative failure. Ultimately though, because information as to just how many juicy pitches players swing at and how many unhittable ones they take is non-existent, though walks are an imperfect measure, they will have to do."
--John Hill writing for The Cub Reporter weblog in 2005

We take a look inside the selection criteria for assembling our Top 50 Prospects list.

For example, BP's Top 50 from 2005, while not without flaws, was better than most. Sure there were pitchers ranked highly (Richie Gardner and Adam Miller) who succumbed to arm injuries. We had thought that Willy Aybar (#34) would develop some power by now and that Edwin Jackson (#45) would improve from his sub-par 2004. Despite those missteps, Baseball Prospectus is proud of the work that went into that list as well as the 2006 version.

With a verifiable cornucopia of prospect lists out in cyberspace, there of course exists a vast array of philosophies governing the compilation of these lists. The king of prospect sites, Baseball America, ranks prospects based on scouting reports, tools, upside, age vs. level of competition and performance. Other sites lean heavily on a player's walk rate. Take, for example, the case of second baseman Travis Denker, in the Dodgers' system. After Denker hit .310/.417/.556 in Low A as a 20-year-old, many sites had him among their top 50 and, in one case, much higher. With a BB/PA rate of .147, Denker has exhibited unusual plate discipline for a young prospect. However, what these lofty rankings ignored were his stone hands, iron glove, .155 EqA upon his promotion to High-A that year, and his PECOTA projections. When different ranking systems rate some pieces of the puzzle higher than other systems, wildly differing outcomes will result.

Wright or Marte, Marte or Wright. I love 'em both. I've put Andy Marte ahead for the moment, because of the 10-month age difference and because scouts seem to like him a lot more, but I really feel strongly that David Wright's as complete a prospect as there is in the game. I'd love to hear comments comparing the two, and Nate, I'd love to see what their PECOTA comps look like. Nobody else is that impressive. Dallas McPherson put up some serious numbers last year, and while some of that was in The Hangar in Rancho Cucamonga, he hit .314/.426/.569 in Arkansas. He doesn't have a great defensive reputation, but it's not terrible either, and he clearly outhit everyone else on this list. I don't know if anyone else deserves Top 50 consideration. I know people love the Greek God of Walks, but he hit .165/.295/.248 in Triple-A, over a 32-game sample. Of course, his full-season OBP was still .446, so... Chad Tracy hit .324 and his defense took a big step forward, but he doesn't do much more than hit singles, and it was Tucson. I respect that he's had two good seasons in a row, but he was in El Paso in 2002, so I'm not sure that means anything either. And as much as I hyped him a year ago, I have to concede that Brendan Harris may not be quite as good as I thought he was. But he's still a better prospect than almost anyone gives him credit for.